Conventionally, hollow cast metal golf club heads are fabricated by, for example, first fabricating two half shells, i.e., an upper shell body and a lower shell body, by for example, the investment casting process, and then welding the two half shell bodies together. This method has the disadvantage of high manufacturing cost. Another method for the fabrication of hollow cast metal golf club heads is the metal die gravity casting method, which uses a sand core to form the hollow cavity of a golf club head. However, by this method, rough surface cast metal golf club heads are obtained, which require further polishing treatment.
The high pressure die casting method has been used recently in the fabrication of cast metal golf club heads, because according to this method, the golf club heads can be integrally fabricated without welding and the fabricated golf club heads have a smooth surface. In addition, golf club heads fabricated by this method usually have high strength, and the traces of the identifications or trademarks to be coined on the club heads can be sharp and be clearly seen.
U.S. Pat. Nos. 5,261,478 and 5,289,865 issued to Donald J. C. Sun disclose two methods of making a golf club head. The disclosed methods include forming a head core consisting of a mixture of particles of sand in a binder; providing at least one core arbor or rod extending into the core and also externally thereof; casting molten lightweight metal about the core and about the arbor to form the shell walls of the golf club head; and removing the core arbor from the head core thereby to form an opening, and removing the head core via the opening.
However, according to this method, as the core is structurally weak, and thus breaks easily, it is not possible to apply higher pressure during the subsequent high pressure die casting process, thereby resulting in the poor quality and strength of the fabricated cast metal golf club heads. Furthermore, according to the method of said patent, although the head core is coated with a barrier coating against the penetration of molten die cast metal into the solidified sand core prior to the molten lightweight metal being cast about the core, the molten metal will still penetrate into the crevices formed between sand particles, thus resulting in the incomplete removal of the core particles, which affects the weight and shifts the center of gravity of the final golf club head. In order to remove the core particles, according to the method of Sun, the binder of the sand core should be incinerated at a high temperature. This additional step will increase the manufactruring cost. Moreover, as sand cores easily collapse, and do not have sufficient strength, a positioning core arbor must be provided extending into the core during the formation of sand cores. This step complicates the fabricating process. Also, by the method as disclosed in said U.S. patent, the hosel opening of the golf club head can not be integrally formed with the club head by using a sand core, and must be formed by using the cylinder slide method. This also complicates the casting molds and thus only one golf club head is produced from one casting mold during one run.